1. Technical Field
The present invention relates generally to high performance dynamometers and more particularly to a roller-type chassis dynamometer having improved the accuracy and repeatability.
2. Discussion
Various roller-type chassis dynamometers have been proposed for inspecting the functions and for monitoring the performance of devices such as automotive vehicles. It is well known in the art that frictional forces acting on the dynamometer can affect the accuracy of the measurements made by the dynamometer. Accordingly, significant resources have been expended to reduce the magnitude of such forces so as to improve the accuracy of the dynamometer.
The efforts in this area primarily focus on the mechanics of the dynamometer structure and the elimination of frictional forces, with the goal being the elimination or quantification of the frictional forces acting upon the dynamometer structure. Despite several recent innovations, the magnitude of the forces acting on the dynamometer structure that affect the accuracy and repeatability of conventional dynamometers remains at a significant level. Complicating matters is that these forces tend to be non-linear (i.e., not proportional to the load applied to the dynamometer) and can vary greatly in magnitude between similarly configured dynamometers. Consequently, it is typically not possible to accurately predict the magnitude of these forces and apply a simple software offset to remove the error associated with the force, rendering it extremely difficult to accurately perform certain tests, such as the monitoring of a vehicle""s tire or drive train losses.
One factor which greatly affects the accuracy and repeatability of the dynometer is related to the manner in which the rotor of the dynamometer is supported. Many conventional dynomometers are designed in a manner wherein frictional forces acting on the rotor of the dynometer are not within a monitored torque or measurement loop (i.e., the frictional forces which resist the rotation of the rotor are not cumulatively monitored by the dynamometer measurement loop or system).
Furthermore, as the magnitude of the frictional forces acting on the dynamometer can vary greatly between otherwise identical dynamometers, a significant portion of the variation in the accuracy and repeatability of the dynomometers stems from factors that are related to their installation. Research has shown that the manner in which the cables and/or hoses are festooned (i.e., routed and supported) to the dynamometer can account for a significant portion of the variation in the forces that affect the accuracy and repeatability of dynamometer measurements.
In this regard, the wires of a conventional dynomometer that couple a control panel to the stator essentially apply a force to the stator that resists rotation of the stator. The force applied by the wire harness results from its unsupported weight that is transmitted to the stator, as well as its resistance to bending. While these forces tend to be small in most situations, the fact that they are typically applied to an exterior surface of the dynomometer stator results in a torque moment that multiplies the effect of these forces several times over. Accordingly, there remains a need in the art for a roller-type chassis dynamometer having a configuration which permits improved accuracy and repeatability.
It is a general object of the present invention to provide a dynamometer apparatus which provides measurements that are more accurate and repeatable.
It is a more specific object of the present invention to provide a dynamometer apparatus which festoons the motor power cables so as to improve the accuracy and repeatability of the dynamometer apparatus.
In one preferred form, the present invention provides a dynamometer apparatus having a roller, an inside-out motor, a measurement loop and a controller for controlling the inside-out motor. The inside-out motor includes a stator, a first set of bearings and a rotor. The stator includes a stator shaft which extends through the rotor and which includes a generally hollow cavity. The rotor is coupled to the roller. The first set of bearings support the rotor and the roller for rotation on the stator shaft about the longitudinal axis of the stator shaft. The measurement loop is established by a load cell which is operatively coupled to the stator shaft. The measurement loop is configured in a manner such that the first set of bearings are within the measurement loop. A plurality of wires couple the controller and the stator wherein the plurality of wires are coupled to the stator at a first end and extend out of the hollow cavity. A second set of bearings couple a base structure and the stator shaft wherein the second set of bearings supports the stator shaft for rotation about a stator axis.